The present invention relates generally to the manufacture of laminated glass and, more particularly, to an apparatus for automatically aligning and accurately directing laminated glass units into a preliminary pressing apparatus employed in a glass laminating operation.
Generally, speaking, so-called laminated safety glass, such as are utilized as windshields for automobiles and the like, comprise two sheets of curved glass and a plastic interlayer interposed therebetween and bonded thereto to form the composite, laminated structure. In the mass production of these laminated glass units, it is customary to first assemble the various laminations in proper superimposed relation to form an assembly or "sandwich", press the sandwich to expel entrained air from between the various layers, and then bond the layers together by subjecting the assembly to the action of heat and pressure.
The preliminary pressing, or so-called "pre-pressing" operation is usually performed in two successive stages. During the first pre-pressing operation, the glass sheets are pressed tightly together to expel any entrained air from the spaces between the layers. Next, the sandwich is subjected to moderate heat sufficient to slightly soften the plastic interlayer and it is then pressed a second time to secure intimate contact between all portions of the plastic interlayer and the adjacent surfaces of the glass sheets. Following the second pressing operation, which also serves to seal the edges of the sandwich, the laminated assemblies are placed in an autoclave where they are subjected to sufficient heat and pressure to securely bond the plastic interlayer to the adjacent glass surfaces. The preliminary pressing operations are necessary to make sure that the glass and plastic interlayers are in sufficiently close contact so that the liquid in the autoclave will not penetrate between the layers of glass and thus interfere with the bonding of the plastic interlayers to the glass.
The apparatus for performing the preliminary pressing operations generally comprises an upper and lower series of pressing rollers arranged in axially parallel, tangentially contacting relation. The rollers are mounted in a cage or frame adapted to be swung arcuately from a sandwich receiving position to a sandwich discharge position. In a typical automated production line, the loosely assembled curved sandwich is advanced horizontally in a longitudinal direction or in a direction normal to the axis of the curvature thereof on a conveyor to the first pre-press section. The leading edge of the sandwich approaches and enters between the opposed pressing rollers along a plane that is generally tangential to each of the rollers which are now in the sandwich receiving position. As the rollers press and pass the sandwich therebetween, they are caused to swing arcuately about a common axis to revolve the sandwich through an arcuate path toward and onto a take-off conveyor.
The longitudinal axis of the sandwich relative to its path of movement on the entry conveyor must be oriented within prescribed limits in order to assure entry of the leading edge of the sandwich into the intended area or restricted target zone between the upper and lower series of pressing rollers. This has conventionally been accomplished by an attendant located at a station immediately forward or upstream of each pre-press section of each laminating production line to manually urge or shift the glass-plastic sandwiches relative to the conveyor into the desired orientation. It can be readily appreciated that such manual operations seriously impair efficiency in a mass production operation, and adds substantially to labor costs. Moreover, the attendant fatigue resulting from the complete concentration and constant surveillance on the part of the attendant in performing such arduous tasks contributes significantly to human error and poor judgment in properly aligning the sandwiches, resulting in glass damage and breakage and further adding to production costs.